The invention relates to an electronic part having gold-plating on its metallic surface.
Gold is widely used in various electronic parts because of its excellent heat resistance, corrosion resistance, solderability, wire bonding property and pellet-bonding property owing to formation of Au-Si eutectic alloy.
Regarding gold-plating, the manufacturing course of an electronic part provided with pads of metallized layers on a ceramic substrate board is described below. After metallized pads have been formed on a ceramic substrate board, Ni-plating is applied to the pad, and leads are connected to the pad which require lead connecting by soldering. Then coatings by Ni-plating, Co-plating and further Au-plating are applied onto a conductor by electric plating in that order. Next, a semiconductor pellet is subjected to die-bonding on the pad. After the pellet is connected to another pad by a wire bonding process, the semiconductor is sealed by glass having a low melting point, or the like. Ni-Co plating as a primer coating for Au-plating herein, is applied to prevent problems which are caused by peeling of Au-plating during seal heating after wire bonding. But in the step of further Co-plating onto a Ni-plated film, hydrogen gas produced during the plating is occluded into plated layers, and thus remains as voids in a Au-Si alloy formed on a pellet upon pellet-bonding by heating at the step of pellet-bonding and the sealing by a low melting point glass, and this results in a serious defect regarding the reliability of the pellet-bonding. Moreover, the Ni-Co-Au plated layer consists of three layers, and consequently strains in the plates between the layers is so large that the problem of peeling of the plated layers may arise when a lead is bent.
In addition, the techniques concerning this field are described in Nos. 34692/80, 4955/83 and 155950/84 of Japanese laid open patents.